But an independent candidate has never won, and is not, in my opinion, ever likely to.

What an independent candidate DOES do is defeat the party which they emerged out of at the election they run in. Ross Perot -- effectively a republican -- significantly helped Bill Clinton defeat GHW Bush. Ralph Nader gave "W" enough of an edge to defeat Gore in a very close race in 2000.

So independents help the other team.

Running as an independent is how you punish a party which you don't think is paying as much attention to you as it should.